FIELD OF THE INVENTION
The invention relates to an optical coupling array having a first substrate with an electrooptical component, a second substrate carrying at least one optical fiber end and formed with a recess open towards the underside thereof and having a mirror face directed towards the optical fiber end, and a third substrate having at least one lens and being disposed between the first substrate and the second substrate, a beam path extending between the optical fiber end and the electrooptical component via the mirror face and the lens.
In optical transmission technology, there is a need for coupling optical fibers and, in particular, monomode optical fibers to electrooptical components (transmitters/receivers) with the highest possible coupling efficiency. The components may be semiconductor lasers, receiving diodes, or optoelectronic integrated circuits. Experience shows that the tolerances needed cannot be adhered to solely by employing high-precision, controlled anisotropic etching techniques in silicon, especially with respect to the etching depths, for example, in the case of trenches or wells with flat bottom surfaces. In the arrangements known heretofore, additional costly adjustments have therefore been necessary.
An arrangement known from the published German Patent Document DE-C1 43 01 456 for coupling an optical fiber to an electrooptical component includes a first substrate which, in a first indentation, receives an edge-emitting laser diode and, in a second indentation, receives an optical imaging element. A coated, light-refracting side wall deflects entering radiation away towards the underside of the first substrate. A second substrate is displaceable arbitrarily with the top side thereof along the underside of the first substrate in a horizontal plane, and is formed with indentations on the underside thereof for receiving the optical fiber therein and for the light-refracting, reflective deflection of the radiation. The conventional coupling array is suitable only for wavelengths of light for which the substrate material is transmissive, because the beam path extends predominantly through the substrate material.
The published European Patent Document EP A2 0 395 854 discloses an optical coupling array which has a first substrate with a first indentation, beginning at the upper side thereof and created by anisotropic etching, wherein an electrooptical component is arranged. Another indentation which is V-shaped has a spherical lens mounted therein, the positioning of which with respect to the laser can be preadjusted to an accuracy of merely 1 to 2 .mu.m. Geometric tolerances of the laser and spherical lens are another factor; height differences (chip height tolerance) of the emitter edge of the laser cause squint angles, because of the imaging properties of the lens. A second substrate carries an optical fiber and rests with its underside on the top side of the first substrate and is displaceable thereon. The beam path extends between the optical fiber end and the components via a mirror face and the lens.
To adapt the distant fields or light spots of the component (with a laser light spot of approximately 2 .mu.m) and the optical fiber end (light spot of about 10 .mu.m), the distance from component to lens (subject distance) is selected to be at a ratio of approximately 1:5 to the distance from the lens to the optical fiber end (image distance). The geometrical tolerances cause a beam offset in front of the lens; this offset is amplified in the ratio of the subject distance to the image distance and causes a considerable worsening of coupling efficiency. At least the second substrate must be used during the mounting process.
The published European Patent Document EP-A2 0 331 331 (FIG. 10) discloses an optical coupling array of the type referred to in the introduction hereto, having a first substrate with an indentation wherein an electrooptical component is disposed. A second substrate is formed with a recess open towards the underside thereof and having a mirror face directed towards an optical fiber end. In a sandwich-like construction, a third planar substrate is disposed between the first and second substrates and contains at least one lens. Further details as to how the three substrates are fixed and how the components received by the substrates are adjusted cannot be found in EP-A2 0 331 331.